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Please help - how can I make "local state" of widget that reflects to change and rebuilds the widget...
# compose
m
Please help - how can I make "local state" of widget that reflects to change and rebuilds the widget when changed? Here I want to change color of rectangle after click on it. But it's not rebuilt. I suppose I don't need global 
@Model
class for this scenario.
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@Composable
fun MyRect(){
    var color = +memo{ Color.Green }
    Clickable(onClick = {
        color = Color.Red
    }) {
        ColoredRect(brush = SolidColor(color), height = 100.dp)
    }
}
l
val color = +state{ Color.Green }
works
you then need to unwrap the state with 
color.value
when needed
g
var color by +state { Color.Green }
l
val*
m
Perfect, works. Thanks! I've seen 
memo
somewhere, but that's probably for different thing.
g
if it will be val, how can you change it
l
You change 
color.value
m
it's 
val
actually. you change its 
value
.
l
not 
color
itself
g
i wrote 
by
, not 
=
m
Hmm. There are two variants. 
var color by +state{ Color.Green }
looks nicer, it doesn't require the 
.value
thing.
g
yeah, i've seen it in sources
l
Yeah, looks better, as they;re also planning to get rid of 
+
m
And who knows for what is 
memo
? šŸ¤”
l
Itā€™s an 
Effect
l
both 
val color = +state { ... }
and 
var color by +state { ... }
will work.
we may at some point lint against 
var
in a composable function that is not introduced by a property delegate. not sure yet though
i prefer the 
var color by ...
version for a couple of reasons, but some people might consider that more magic, so up to you
šŸ‘Œ 1
l
It looks nicer indeed
f
I say to get rid of the other way
Having multiple ways of doing the same thing is just confusing
m
Proper way is 
var ... by
. You're interested in your variable, not the delegate that is behind providing its value.
šŸ‘† 1
f
and also wars about the right way of doing it are not nice
l
itā€™s definitely something worth considering
in general i agree with ā€œmultiple ways of doing the same thing is badā€
but itā€™s hard to know where you draw the line hereā€¦.
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val x = a
val y = x.first
val z = x.second
vs
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val (y, z) = a
should kotlin make the 1st way impossible?
l
YES
šŸ§Œ 3
f
Hmm, I wrote a long message about why that's not the same thing, but that got deleted because of internet connectivity. Anyway, the conclusion is that at the very least there should be an inspection to use the 
by
syntax and to only use the 
by
syntax in official examples.
l
Why? What if I need a 
State
object?
f
Why would you need a 
State
object?
l
Maybe I want 
component1
and 
component2
f
Maybe
But why would you need a State object?
l
If you donā€™t have the state object you canā€™t get 
compoent1
and 
component2
of 
State
Btw, I already said the 
by
solution looks cleaner and Iā€™d use that, but as @Leland Richardson [G] said itā€™s hard to know where to force something
f
oh, you mean 
(someState,setSomeState)
l
yes
f
Why would you use this syntax over using 
by
?
Right now it seems to me like that should begone too
g
Copy code
val state = +state { false }
Checkbox(checked = state.value, onCheckedChange =    state.component2())
var checked by state
f
```
That's... unreadable
I don't think that's desired
I would rather read
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var state by state { false }
Checkbox(checked = state.value, onCheckedChange  = {state = it})
But I could see
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val (state,setState) = state { false }
Checkbox(checked = state.value, onCheckedChange =    setState)
But is this tiny synctactic sugar really worth having 3 ways of doing the same thing?
l
Well thatā€™s 2 ways of doing the same šŸ˜›
f
What do you mean? You can 1) do
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val (value,setValue)  = state { false }
2)
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val value = state {false}
3)
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var value by state { false }
l
Yeah, the second one is bundle into the first
What I meant was: 
= +state{}
could be used for 
1.
, 
by
could not. Maybe thatā€™s the reason for having both of them šŸ™‚
a
the first one is a lot like react hooks
l
Well thatā€™s because Compose is influenced by React as well, alongside by Flutter, Vue.js, Litho
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